1. Field of the Invention
The present invention relates to a coil assembly for an electromagnetic valve to be used in a vehicular hydraulic control circuit and, more particularly, to a coil device to be used especially in a linear solenoid or an electromagnetic valve.
2. Description of the Prior Art
FIG. 13 is a section showing an electromagnetic coil assembly of the prior art before forming the resin molding around same; FIG. 14 is a view taken in the direction of arrows A--A of FIG. 13; FIG. 15 is a section showing the electromagnetic coil device after the resin-molding operation; and FIG. 16 is a view taken in the direction of arrows B--B of FIG. 15.
The electromagnetic coil device to be embedded in molding resin is prepared as shown in FIGS. 13 and 14, by winding the electromagnetic coil 2 around the coil bobbin 1 and by fixing a connector terminal 4 and a ground terminal 5 to one end of the coil bobbin 1. Moreover, the leads 3 of the electromagnetic coil 2 are connected with the individual fusing portions 6 of terminals 4 and 5, and an insulating tape (although not shown) is wound on the outermost circumference of the wound electromagnetic coil 2. Moreover, the electromagnetic coil 2 wound on the coil bobbin 1 is sometimes impregnated with varnish for its protection. The connector terminal 4 of the electromagnetic coil device thus assembled is bent 90.degree. (as indicated by dotted lines in FIG. 13), and the whole device is coated with a molding resin 7, excepting portions of the connector terminal 4 and the ground terminal 5, as shown in FIGS. 15 and 16, to produce the resin-embedded coil device.
However, it is difficult to wind the insulating tape properly to protect the electromagnetic coil. Moreover, unless the insulating tape is properly positioned upon wrapping, it may cause damage to the electromagnetic coil and/or tear or break the insulation when the coil bobbin is covered with the metal casing. If impregnation with varnish is used to protect the electromagnetic coil and if the coil wrapping is not properly positioned, the varnish coating of the electromagnetic coil may also be damaged when the coil bobbin is assembled with the metal casing, creating a possibility of insulation failure.
With such a resin-covered coil device, moreover, the electromagnetic coil is subject to thermal shock. Further, the heat generated by the electromagnetic coil is not transferred efficiently by the molding resin, creating a problem of heat dissipation.